Optical laminate, optical element and liquid crystal display device

Abstract

An optical laminate having layer A having a resin having a negative intrinsic birefringence and at least one layer B having a transparent resin, having substantially no orientation and laminated at least on one face of layer A and satisfies a relation |Re(A)|>|Re(B)|, wherein Re(A) and Re(B) represent in-plane retardations of layer A and layer B, respectively, measured with light having a wavelength of 400 to 700 nm, an optical element having a laminate of the optical laminate and a polarizer plate, and a liquid crystal display device using at least one sheet of the optical laminate. In the liquid crystal display device, optical compensation can be made in accordance with the mode of the liquid crystal display by the three dimensional control of the refractive index, and the liquid crystal display device provides an image display with liquid crystals exhibiting small change in the phase contrast depending on the viewing angle.

1. An optical laminate (optical laminate C) which comprises a layer (layer A) comprising a resin having a negative intrinsic birefringence and at least one layer (layer B) comprising a transparent resin, having substantially no orientation and laminated at least on one face of layer A and satisfies a relation |Re(A)|>|Re(B)|, wherein Re(A) and Re(B) represent an in-plane retardation of layer A and an in-plane retardation of layer B, respectively, measured with light having a wavelength of 400 to 700 nm, wherein the optical laminate satisfies a relation Σnz>Σny−0.002, wherein Σnz represents a refractive index in a direction of a thickness and Σny and Σnx represent refractive indices in two directions which are perpendicular to the direction of a thickness and perpendicular to each other of optical laminate C measured with light having a wavelength of 550 nm, and Σnx, Σny and Σnz satisfy relations Σnx<Σny and Σnx<Σnz; and wherein the optical laminate satisfies a relation Tg(A)>Tg(B)+20, wherein Tg(A) and Tg(B) represent glass transition temperatures in ° C. of the resin of layer A and the resin of layer B, respectively. 
     
     
       2. The optical laminate according to  claim 1 , wherein |Re(B)| is 20 nm or smaller. 
     
     
       3. The optical laminate according to  claim 1 , which satisfies a relation Re(450)>Re(550)>Re(650), wherein Re(450), Re(550) and Re(650) represent in-plane retardations at wavelengths of 450 nm, 550 nm and 650 nm, respectively. 
     
     
       4. The optical laminate according to  claim 1 , wherein an unevenness in a thickness of layer A is 3.0% or smaller of an average thickness of layer A. 
     
     
       5. The optical laminate according to  claim 1 , wherein the resin having a negative intrinsic birefringence is a resin selected from a group consisting of vinyl aromatic polymers, polyacrylonitrile polymers and polymethyl methacrylate polymers. 
     
     
       6. The optical laminate according to  claim 1 , wherein the resin having a negative intrinsic birefringence is a vinyl aromatic polymer. 
     
     
       7. The optical laminate according to  claim 1 , wherein the resin having a negative intrinsic birefringence is a resin selected from a group consisting of polystyrene and copolymers of styrene and maleic anhydride. 
     
     
       8. The optical laminate according to  claim 1 , wherein the transparent resin is a resin having an alicyclic structure. 
     
     
       9. The optical laminate according to  claim 1 , wherein the transparent resin is a norbornene polymer. 
     
     
       10. The optical laminate according to  claim 1 , wherein the transparent resin is a hydrogenation product of a ring-opening polymer of a norbornene monomer or a hydrogenation product of a ring-opening copolymer of a norbornene monomer. 
     
     
       11. The optical laminate according to  claim 10 , wherein the resin having a negative intrinsic birefringence is a copolymer of styrene with maleic anhydride. 
     
     
       12. The optical laminate according to  claim 1 , wherein the transparent resin has a tensile elongation at break of 30% or greater. 
     
     
       13. The optical laminate according to  claim 1 , wherein the layer comprising a transparent resin and having substantially no orientation (layer B) is laminated on both faces of the layer comprising a resin having a negative intrinsic birefringence (layer A). 
     
     
       14. The optical laminate according to  claim 1 , wherein an adhesive layer is disposed between the layer comprising a resin having a negative intrinsic birefringence (layer A) and the layer comprising a transparent resin and having substantially no orientation (layer B). 
     
     
       15. The optical laminate according to  claim 14 , which satisfies relations Tg(A)>Tg(D) and Tg(B)>Tg(D), wherein Tg(D) represents a glass transition temperature or a softening point in ° C. of an adhesive in the adhesive layer. 
     
     
       16. An optical element comprising a laminate of the optical laminate described in  claim 1  and a polarizer plate. 
     
     
       17. A liquid crystal display device which uses at least one sheet of the optical laminate described in  claim 1 . 
     
     
       18. The liquid crystal display device according to  claim 17 , wherein said liquid crystal display device comprises a liquid crystal cell of in-plane switching (IPS) mode. 
     
     
       19. The optical laminate according to  claim 1 , wherein the optical laminate C is obtained by co-stretching an unstretched laminate comprising an unstretched resin layer comprising the transparent resin and having substantially no orientation and an unstretched resin layer comprising the resin having a negative intrinsic birefringence, said unstretched resin layer comprising the transparent resin and having substantially no orientation being laminated on at least one face of the layer comprising the resin having a negative intrinsic birefringence. 
     
     
       20. The optical laminate according to  claim 19 , wherein the laminate is co-stretched at a temperature of from Tg(A)−10 (° C.) to Tg(A)+20 (° C.). 
     
     
       21. The optical laminate according to  claim 20 , wherein glass transition temperatures Tg(A) and Tg(B) in ° C. of the resin of layer A and the resin of layer B, respectively, satisfies a relation: Tg(B)+30>Tg(A)>Tg(B)+20. 
     
     
       22. The optical laminate according to  claim 19 , wherein the laminate is obtained by a molding process by coextrusion of the resin having a negative birefringence and the transparent resin. 
     
     
       23. A process for producing an optical laminate (optical laminate C) which comprises a layer (layer A) comprising a resin having a negative intrinsic birefringence and at least one layer (layer B) comprising a transparent resin, having substantially no orientation and laminated at least on one face of layer A and satisfies a relation |Re(A)|>|Re(B)|, wherein Re(A) and Re(B) represent an in-plane retardation of layer A and an in-plane retardation of layer B, respectively, measured with light having a wavelength of 400 to 700nm,
 wherein the optical laminate satisfies a relation Σnz>Σny−0.002, wherein Σnz represents a refractive index in a direction of a thickness and Σny and Σnx represent refractive indices in two directions which are perpendicular to the direction of a thickness and perpendicular to each other of optical laminate C measured with light having a wavelength of 550 nm, and Σnx, Σny and Σnz satisfy relations Σnx<Σny and Σnx<Σnz, 
 wherein said process comprises: 
 laminating the layer comprising the transparent resin and having substantially no orientation on at least one face of the layer comprising the resin having a negative intrinsic birefringence to form an unstretched laminate, and 
 costretching the formed unstretched laminate. 
 
     
     
       24. A process according to  claim 23 , wherein the unstretched laminate is co-stretched at a temperature of from Tg(A)−10 (° C.) to Tg(A)+20 (° C), and wherein Tg(A) and Tg(B) represent glass transition temperatures in ° C. of the resin of layer A and the resin of layer B, respectively.